1. Field of the Invention
The invention relates generally to seimsic energy vibrators and, more particularly, but not by way of limitation, it relates to an improved vibration apparatus having selectively controllable drive cylinder volume for frequency range adaptability.
2. Description of the Prior Art
Prior art in point is U.S. Pat. No. 4,106,586 in the name of Stafford, property of the present assignee, which teaches a hydraulic siesmic vibrator wherein the reaction mass includes an axial drive cylinder that is variable between two positions, a maximum and a minimum cylinder volume. On the order of the present invention, the Stafford vibrator utilizes movable end sleeves disposed in opposite ends of the hydraulic cylinder and these, in turn, are hydraulically controllable between two positions, simultaneously, relative to the height of the cylinder. The present invention is directed to a continuously variable cylinder volume control and the capability of achieving optimum fluid compressibility factor throughout a selected frequency range of operation, and this is particularly desirable at higher seismic frequencies on the order of 250 Hertz and up.